Every writer goes through a stretch when good ideas simply aren't forthcoming. Most have ideas, but they tend to dismiss them as terrible, rehashes of a more famous story or something not worth writing.
These same writers will tell you going through a creative dry spell is one of the most frustrating things a writer can face. Without an idea, there essentially is no writing. It's one of the many forms of writer's block. (Though I personally find myself more irritated when I've started on something and get stuck with it.)
Thankfully, there are a ton of places to turn when you find yourself completely out of fresh ideas. Here are a few:
Find a Prompt
Some writers may tend to frown upon using prompts. It's someone else "idea" so to speak. You'll probably never find yourself getting such works published, and that alone is enough to make writers shy away from using them.
The point of using a prompt is to kick start your writing, to get your creative juices flowing again. The prompt is just the start. Most prompts (depending on where you find them) tend to give you a ton of space to mold characters, setting or plot.
I personally belong to a group on Wattpad which gives out a one-word prompt for each weekend. The only "rule" is that the work come in around 500 words in length. Otherwise, it's complete freedom to interpret the word in a way which fits my idea. I have found it very helpful as it is the one time each week where I know I'll have an idea to write about. The group is very responsive and I get a ton of feedback as well.
Those works may never be published anywhere else, but that isn't the point. I can pretty much count on writing 500 words, in my own creative story, each week. It may not be a lot, but it's enough to make me feel like I'm making headway as a writer.
Other than Wattpad, you can simply use Google to find prompt lists. Some are tied to contests or submissions, others are just for fun. I enjoy the group setting as it gives me feedback as well, but you may find you just want to do things on your own terms.
As odd as this sounds, I have gotten TONS of ideas from Wikipedia.
I tend to write a lot of historical fiction, so the translation into a story is often rather easy. You find some historical event and write some sort of tangent to it: Add dialogue to a poorly-recorded event; make the real historical event a background element to your story; or use the event as the basis for a completely new story.
Also on the menu, if you're a sci-fi writer, is a wealth of ideas for alternate history. These are especially fun when you examine some relatively obscure historical event, then try to think about the butterfly effect of things unfolding differently. While the alternate history genre tends to focus on major historical events turning out differently (WWII or the American Civil War), it can be more fun to explore something well off the beaten path, such as if George Washington had received the British Army commission he asked for.
The best thing about Wikipedia is the sheer volume of things to read on it. It doesn't have to be a historical event to inspire you. Perhaps it is an unusual place (such as Mt. Athos in Greece) or an extinct animal or even an intriguing name.
My ever-growing collection of short and flash fiction stories is comprised of at least 70 percent Wikipedia-inspired stuff. At the very least, I learn something new even when inspiration doesn't strike me.
What You Thought You Heard
So it might be borderline silly, but taking a misheard statement and running with it might just be the best thing to get you started on your stalled writing.
We've all had times when someone has said something to us and our mind hears relative nonsense. We either ask for clarification or we try to sort it out in our head, as to what the statement actually was.
But it can be equally fun to say what you think you heard aloud, and perhaps jot it down for future use. I have a nice list of weird things I thought I heard from my children and my wife. Some of the better ones include my son's mispronouncing of the Grim Reaper into a character called the Gym Reaper (perhaps a person who excels in physical education?) and "Pirates with Jetpacks" (which came from some garbled statement by my wife, which I no longer remember).
The point is, you can find some fun jumping points for starting a story by stringing together the nonsense you thought you heard.
Fictionalizing One of Your Own Memories
You remember a lot of stuff. Most of it is boring and wouldn't make compelling reading if the true version were told. But there's no rule about using it as inspiration for a nice fiction story. After all, Hollywood thrives on the "Based on True Story" types of movies which often bear little resemblance to the actual event. (Braveheart being a classic -- and massive -- offender.)
Start with the time you got lost in the department store and went to the service desk to have them page your mother. In real life, your mom came up, probably mildly embarrassed and annoyed and got you. Not the most exciting story. But if your mom vanished into thin air, or she mysteriously developed amnesia and doesn't know you're her child...well, that's the start of a good yarn.
As long as you're not pawning off your story as total non-fiction, you have license as a writer to take a real event and add spicier elements to it. It's an easy way to get started on something, since you already know the entire story as it actually played out. You can twist around the ending. Throw in a scene with your annoying sister to add tension. Maybe a brush with fame or some mortal peril. It's up to you.
The World Around You
It's obvious inspiration can strike anywhere at any time. If you're stuck creatively, the best advice I can give to get better at observation. This includes reading, listening and looking at your surroundings. Weird business names start to show up. You become intrigued about why someone felt the need to put up a deer crossing sign on a particular stretch of highway.
Questions are almost always at the root of a good idea, particularly the "what if..." kind. You'll find a good idea in no time if you start down that path.
And what if you don't find inspiration, wracking your brain but coming up empty? I'd say that could make a good story, but Stephen King already beat you to it.